Biology subjects

Kulig, W.

Publications and source records attributed to Kulig, W..

4 recordsLinked to original sources

bioRxiv2026

Activation mechanism of class A GPCRs: machine learninganalysis of experimental structural databases

Recent advances in cryo-electron microscopy and cryo-electron tomography have dramatically increased the number of class A G protein-coupled receptor (GPCR) structures, especially in previously inaccessible G protein-bound, active-like conformations. The increased structural diversity provides a unique opportunity to explore the conformational landscape underlying GPCR activation. To this end, we developed a machine learning (ML) framework that utilizes experimental structural data to elucidate the activation dynamics of class A GPCRs. We find that receptors can populate both inactive and active-like conformations even in the absence of ligand or G protein, providing a structural basis for agonist-free basal activity. Agonist binding shifts this conformational ensemble towards the active state but does not fully stabilize it. Instead, a stable active state is only established upon G protein binding, which locks the receptor in its active conformation. These results support a hybrid activation mechanism in which ligand binding follows conformational selection, while transducer engagement is governed by induced fit. Beyond clarifying class A GPCR activation, the openly available and modifiable ML framework provides a practical tool for analyzing newly determined structures, investigating the mechanisms of action of other GPCR classes and protein families, and guiding structure-based drug discovery in important pharmacological superfamilies. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=71 SRC="FIGDIR/small/714415v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@19d1327org.highwire.dtl.DTLVardef@1549782org.highwire.dtl.DTLVardef@a6dfaaorg.highwire.dtl.DTLVardef@1a650ce_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Unraveling the GM1 specificity of Galectin-1 binding to lipid membranes

Galectin-1 (Gal-1) is a galactose-binding protein involved in various cellular functions. Gal-1s activity has been suggested to be connected to two molecular concepts, which are however lacking experimental proof: a) enhanced binding affinity of Gal-1 towards membranes containing monosialotetrahexosylganglioside (GM1) over disialoganglioside GD1a and b) cross-linking of GM1s by homodimers of Gal-1. We provide evidence about the specificity and the nature of Gal-1 interaction with model membranes containing GM1 or GD1a, employing a broad panel of fluorescence-based and label-free experimental techniques, complemented by atomistic biomolecular simulations. Our study demonstrates that Gal-1 binds indeed specifically to GM1, and not to GD1a, when embedded in membranes over a wide range of concentrations (i.e., 30 nM to 10 M). The apparent binding constant is about tens of micromoles. On the other hand, no evidence of Gal-1/GM1 cross-linking was observed. Our findings suggest that cross-linking does not result from sole interactions between GM1 and Gal-1, indicating that in a physiological context, additional triggers are needed, which shift the GM1/Gal-1 equilibria towards the membrane-bound homodimeric Gal-1. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=198 SRC="FIGDIR/small/614102v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@c4ff01org.highwire.dtl.DTLVardef@141c82eorg.highwire.dtl.DTLVardef@1bd7c0borg.highwire.dtl.DTLVardef@11af49e_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Adipogenin Dictates Adipose Tissue Expansion by Facilitating the Assembly of a Dodecameric Seipin Complex

Adipogenin (Adig) is an evolutionarily conserved microprotein and is highly expressed in adipose tissues and testis. Here, we identify Adig as a critical regulator for lipid droplet formation in adipocytes. We determine that Adig interacts directly with seipin, leading to the formation of a rigid complex. We solve the structure of the seipin/Adig complex by Cryo-EM at 2.98[A] overall resolution. Surprisingly, seipin can form two unique oligomers, undecamers and dodecamers. Adig selectively binds to the dodecameric seipin complex. We further find that Adig promotes seipin assembly by stabilizing and bridging adjacent seipin subunits. Functionally, Adig plays a key role in generating lipid droplets in adipocytes. In mice, inducible overexpression of Adig in adipocytes substantially increases fat mass, with enlarged lipid droplets. It also elevates thermogenesis during cold exposure. In contrast, inducible adipocyte-specific Adig knockout mice manifest aberrant lipid droplet formation in brown adipose tissues and impaired cold tolerance.

cell biology↗

bioRxiv2022

Dissecting the mechanisms of environment sensitivity of smart probes for quantitative assessment of membrane properties

The plasma membrane serves as a crucial platform for a multitude of cellular processes. Its collective biophysical properties are largely determined by the structural diversity of the different lipid species it accommodates. Therefore, a detailed investigation of biophysical properties of the plasma membrane is of utmost importance for a comprehensive understanding of biological processes occurring therein. During the past two decades several environment-sensitive probes have been popular tools to investigate membrane properties. Although these probes are assumed to report on membrane order in similar ways, their individual mechanisms remain to be elucidated. In this study, using model membrane systems, we studied the probes Pro12A, NR12S and NR12A in depth and examined their sensitivity to parameters with potential biological implications, such as the degree of lipid saturation, double bond position and configuration, phospholipid headgroup and cholesterol content. Applying spectral imaging together with atomistic molecular dynamics simulations and time-dependent fluorescent shift analyses, we unravelled individual sensitivities of these probes to different biophysical properties, their distinct localizations and specific relaxation processes in membranes. Overall, Pro12A, NR12S and NR12A serve together as a toolbox with a wide range of applications allowing to select the most appropriate probe for each specific research question.

biophysics↗